1. Field of the Invention
The present invention relates to an elastic roller for an electrophotographic apparatus or the like, and a process of manufacturing such an elastic roller.
2. Description of the Prior Art
Elastic rollers of various different constructions have been proposed for use on electrophotographic apparatus. A rubber roller formed by coating a roller core with an elastic rubber layer is a typical roller for such a purpose. When soft elasticity is essential, a rubber roller is formed by coating a roller core with a sponge rubber layer and coating the circumference of the sponge rubber layer with a heat-resistant elastic layer. Such a roller is disclosed, for example, in Japanese Patent Provisional Publication (Kokai) Nos. 58-23072, 59-37580 and 59-61864. Such a known elastic roller is fabricated through steps of applying an adhesive to the circumference of a roller core, putting a prefabricated sponge rubber tube on the roller core, coating the circumference of the sponge rubber tube with an elastic resin layer, and grinding the elastic resin layer to finish the elastic roller. Another known elastic roller is fabricated through steps of wrapping around a roller core with a masticated rubber stock containing a gas producing ingredient, making the rubber stock foam within a mold, and covering the circumference of the rubber layer with an elastic resin. However, these elastic rollers require a complicated manufacturing process and a high manufacturing cost due to expensive materials. A third known elastic roller is fabricated through steps of wrapping around a roller core with a masticated rubber stock containing a gas producing ingredient, and making the rubber stock form and vulcanizing the foamed rubber within a mold so that a smooth skin layer is formed. Although this elastic roller can be manufactured at a comparatively low manufacturing cost, free toner remaining on a recording sheet and paper powder is liable to adhere to the surface of the elastic roller entailing offset and roller lap-up after the elastic roller has passed about 10,000 recording sheets because the elastic roller has poor release property and the outer surface of it is as glossy and smooth as mirror. If this elastic roller, i.e., the elastic sponge rubber roller with skin, is impregnated with silicone oil to solve such a problem by enhancing the release property, the silicone oil contained in the skin layer swelled with the silicone oil is transferred to recording sheets entailing the contraction and deformation of the foam rubber layer, so that recording sheets are liable to be creased by the elastic roller. Furthermore, the release property of the skin layer becomes ineffective in a short time of operation.
Japanese Patent Provisional Publication (Kokai) No. 63-139380 proposes a pressure roller for fixing. This fixing pressure roller is equipped with a coating layer formed by coating outer surface of a rubber sponge roller with a mixture of a fluororubber and a silicone resin or a fluororesin and hardening the coating of the mixture. However, the coating is worn and removed in the long run by recording sheets and, finally, the skin layer is exposed unavoidably entailing the foregoing problems.